Beauty and the Beasties
Pollinating insects and flowering plants have been co-evolving for over 70 million years. A few elaborate symbiotic relationships aside, the vast majority or plants, whether its bulbs, annuals, perennials, trees or shrubs are essentially open to pollination to whichever ‘creature’ lands on its flower at the right place, at the right time. But the intricacies are fascinating. The adaptations between plant and pollinator are simply mind-blowing.
pollinator | ˈpɒlɪneɪtə | noun
an insect or other agent that conveys pollen to a plant and so allows fertilisation: “bees are effective pollinators of fruit and vegetables."
Just a snippet of basic pollination biology…
Flowering plants produce pollen within the flower. Pollen is essential to the reproductive cycle and consists of microscopic grains containing the genetic material needed to fertilise plants. Plants also produce nectar within the flower. Nectar is a sugary fluid and a potent food source for cold-blooded insects and other invertebrates. Therefore, nectar is the perfect lure in which to attract potential pollinators that will help spread that genetic material. Pollen itself is also a quality protein food source for many species and bees will collect pollen on their legs or abdomens (pollen sacks) as food for their larvae.
In one ingenious way or another (and believe me when I say ingenious!), the pollen is deposited on a visiting pollinator by the anthers (male / stamen) of one flower and when that same pollinator visits another flower of the same species and rummages around for the nectar, that pollen is rubbed on to stigma (female / pistil) and fertilisation has been completed. The flower can set seed and the plant reproduces. Voila!
The bare necessities
Being cold-blooded, insects and other invertebrates need food and warmth to sustain life. Many species hibernate in burrows or cocoons during winter and emerge in spring. Others will lay their eggs in nest cells to overwinter and emerge as adults the following year. Some butterflies and moths overwinter as adults in a dormant state, but many overwinter as caterpillars or in a chrysalis. When our pollinators emerge after winter, they need fuel, urgently. This is why it’s so critical to grow early flowering plants, like hellebores, snowdrops, crocus, etc.
Going native
A pollinator garden doesn’t mean you’re restricted to native plant species alone, although it’s a great place to start. Native species will have evolved adaptations to cope with your local climate and soil type as well as providing the right flower shapes, nectar and pollen for local pollinator species.
Looking at my own garden borders, there are wild primrose, red and white campion, native aquilegia and foxgloves, forget-me-not, cow parsley, sweet woodruff, lily of the valley, and wild carrot. In the wilder areas, thistles, nettles, brambles, dandelion, creeping buttercup, and alkanet are most dominant.
It’s true that the commonplace plants that we find in all garden centres are bred from plants sourced from across the globe. What makes them good or bad for pollinators boils down to nectar, pollen production and accessibility to both. Not which corner of the Earth they originate. So let’s not be xenophobic!
Nectar is nectar! That being said, you can find beautiful cultivars of native species in the garden centres. Anthriscus ‘Ravenswing’, Cornflowers, Achilleas, Primulas, and a myriad of Foxgloves (Digitalis) spring to mind. In the case of many modern cultivars, nectar and pollen production are intentionally bred out in favour or more petals or bigger blousy blooms. It’s actually these cultivars which require more scrutiny, despite what the plant labels may say. They are without doubt seductively beautiful, especially those gorgeous ruffled doubles, but definitely low-scoring for pollinators. We’ll come back to garden plants in the next chapter.
The unbelievable cleverness of plants
Alongside a refined understanding of colour, form, and chemical compositions of aroma (VOC), recent scientific research has discovered the myriad of ways plants have evolved fascinating evolutionary adaptations to maximise pollination.
Quite frankly, if none of the following adaptations amaze and astonish you, then it’s time to pack up the tool shed and check out, because you are missing something truly wondrous!
- Ever wondered how bees manage to cling onto flowers in windy conditions? I have! When viewed under extreme magnification, you can see that some flower petals are covered with backward pointing conical structures to help insects grip firm, like velcro!
- Why do some plants seem more popular than others? It could be warmth? Thermal imaging cameras reveal that some flowers generate heat (a process called thermogenesis) at the point where nectar flows, rewarding pollinators with both heat and food - a powerhouse combination for cold-blooded invertebrates. "The majority of flowers examined, including many common in gardens, such as poppies and daisies, had complex patterns of heat across their petals, echoing the colourful patterns that we see with our own eyes. On average these patterns were 4–5°C warmer than the rest of the flower, although the patterns could be as much as 11°C warmer." Read more here
- Remember how we used to rub inflated balloons on our clothes as kids and watch our hair rise as the balloon is brought closer…? Well, a recent scientific discovery has revealed yet another remarkable adaptation in the use of electric fields (static). Whereas the exoskeleton of many invertebrates is positively charged (+) plants and flowers are negatively charged (-). As the pollinator comes into contact with the stamen, pollen transfers and sticks onto the positively charged exoskeleton. Read more here
- How do bees seem to know if a flower has already been emptied of its nectar? Using the same ‘static’ principle, it’s also been shown that some bees and hoverflies can sense recent pollination by detecting the strength or weakness of the flowers electric field by the way their thoracic hairs are deflected (like with the balloon). Read more here
- Conversely, in some species of plant, negatively charged flowers can detect the presence of a positively charged field (created by a pollinator) and release more floral volatile organic compounds (VOC) to lure them in to pollinate. Read more here
- Many flowers have markings of one form or another. Spots, stripes, colourful falls, etc. Some of these we can see, some we cannot. Some flowers, especially those purple, red, and yellow flowers, glow vividly in ultraviolet light. Although invisible to us, UV is visible to bees. Having a neon decorated landing pad is an effective adaptation for attracting those fast flying insects.
Are you not amazed?
The fact that some ‘flowers’ smell like rotting flesh to lure in its specialist flies, or mimic an insect, convincing a clueless bee it’s found a mate, seems rather dull compared to static charged pollen and neon heated flowers!
Other than colour and perfume, probably the most obvious plant adaptation (to us gardeners) is the flower shape, capable of either hiding or revealing the nectar and pollen, to allow or exclude particular species of pollinator. Tubular flowers like foxgloves and honeysuckle require the longest tongue/proboscis of all our bees, the garden bumblebee, Bombus hortorum, compared to daisy-type flowers or umbellifers that are open to all comers. Some absolute giants of the plant world are pollinated by the tiniest flies. Others rely on hummingbirds, bats, even lemurs!
I have to say it has been absolutely mind-blowing, researching and learning about these adaptations and trying to understand these unfathomable research papers. I have to keep to the ‘abstracts’ as the science is well above my pay grade! I sincerely hope you’ve found them enlightening too! Coincidentally, while writing this, Gardeners World TV aired two episodes discussing these scientific discoveries which I have linked here.
Coming up…
Flowering 365 days a year? How you can have plants flowering successionally all year round. We’ll be looking at plant recommendations, what plants I have used, where and why? How we can improve the diversity and extend those pollinator friendly plants through the season and into the lawn and the vegetable garden.
Add comment
Comments